A method of taking a stereoscopic image using an image capturing device which includes a plurality of capturing units is known. In a stereoscopic image which is obtained by the capturing device, stereopsis can be performed by displaying a left eye image for the left eye, and a right eye image for the right eye of a viewer, respectively, in a stereoscopic display apparatus. This method is a method in which parallax which occurs between images which are obtained by photographing the same object from different viewpoint positions is used. It is possible to measure a distance to an object using triangulation when the parallax, a distance between two viewpoint positions which are photographed by the image capturing device, and camera parameters of the image capturing device are known. For example, in PTL 1 which is described below, a method of measuring the length between two designated points on an object using a stereo camera is disclosed.